The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 165 degrees of the sun's apparent longitude. It is a sectional term, a jie, one of the twelve that fall in the odd positions of the twenty-four and open the twelve solar months. The sectional terms and the major terms alternate strictly around the year, so a jie is always followed by a zhong fifteen degrees later.
The system travelled with the Chinese calendar. Japan, Korea and Vietnam all adopted the twenty-four terms and kept their own readings of the same names, and the terms remain in use in each. In 2016 the twenty-four solar terms were inscribed on the UNESCO Representative List of the Intangible Cultural Heritage of Humanity, on the ground that they remain a living framework for agricultural and everyday practice rather than an obsolete scheme.
Bailu, white dew, is the first of two dew terms, with Hanlu, the cold dew, a month later. Dew forming on the ground in the morning is an observable and unambiguous sign, and the two dew terms are among the clearest examples of the principle behind the whole system: a solar term names a point in the sun's course, and its name records what that point looked like from the ground in the region where the calendar was fixed.